Iron or iron-based powders are used in numerous applications and fields of technology. The powder particles with ability to form shaped bodies under pressure are utilized in production of pressed and sintered metal parts. Its chemical reactivity is utilized in various chemical processes. Iron or iron-based powders may also be used as additives in coatings of manual metal arc electrodes or in various friction materials, such as in brake pads.
A brake pad, and in particular the friction material of the brake pad for transportation vehicles, must fulfill a great number of requirements and also must satisfactory work in different environments, in wet and dry conditions, at high and low temperatures, at high thermal load etc. The friction material of a brake pad contains a great number of powdered substances, each of them playing an important role, either individually or in combination with other substances, the role however is not always possible to accurately define or quantify. For that reason, the development of friction materials for a brake pad is still very much based on trials and sometimes it is characterized as an art.
One substance frequently used in the friction material is copper powder, which among others play a role for the heat dissipation during braking and for the stable friction at high temperature environment.
However, the use of copper is being restricted in brake pads due to environment and health concerns. When the copper is removed from the brake pad formulation, great challenges are presented how to solve issues such as thermal fade or excessive pad and or rotor wear during use of the brake pad. Several attempts have been done to find a suitable replacement with limited success. For example, iron powder has been used as a replacement for copper but it has been encountered that hard and abrasive particles during the use of the brake pad can be formed, because graphite, a very common substance used in brake pad formulations, can diffuse into the iron to form cementite containing phases by the friction heat. The cementite containing phases are hard phases compared to the original iron powder that has a ferrite phase, a soft phase with hardness close to copper. Such hard phases can cause unstable friction and high pad and or rotor wear. Thus, there is a need to find suitable alternatives to replace the copper powder in brake pads.